1. Field of the Invention
The present invention relates to cargo container handling gantry cranes. More particularly, it relates to an improvement in the wire rope reeving system for the cargo container transport trolley of such cranes. Specifically, it relates to a wire rope reeving support system for gantry cranes in which the rope systems which perform load hoist and trolley traversing operations are supported at least mid-span of the maximum rope suspension length of the crane.
2. Description of the Prior Art
The cargo container handling gantry cranes which benefit from the improvement provided by the present invention are those which are arranged in the operating configuration to extend over a longitudinal expanse of ground, dock, or water to transfer cargo containers horizontally from one deposition area to another. The heaviest of such gantry cranes are usually located dockside in shipping ports around the world in the form of bridge cranes or gantry cranes. Dockside gantry cranes generally have either a horizontal sliding boom or a cantilever boom, the latter of which can usually be raised by rotating it around its inboard end. An example of this latter type of crane which is more prevalent is disclosed in U.S. Pat. No. 5,765,981 and was developed by the assignee of the present invention. Other types of large gantry yard cranes are located in large cargo container storage or transfer areas. These are long span bridge cranes and are typically supported by vertical structures located inboard from both ends of the crane gantry on rail-mounted wheels.
Reference is made to FIG. 1 of the drawings for a representation of the '981 type of gantry crane having a cantilevered rotatable boom 11 projecting from the crane superstructure 13. It is supported on crane truck wheels 15 which are mounted on dock rails which run parallel to the edge of the quay. The superstructure supports a horizontal gantry 17 disposed generally mid-height thereon at an elevated location above the cargo container pickup and deposition areas 19. The gantry is supported from below by the main legs of the superstructure. In the cantilevered rotatable boom design, sheaves are disposed at the pinnacle 21 of the superstructure of the crane to guide wire rope reeving 23 which is used to rotate the outboard or cantilevered end of the boom to the upright raised stowed position. The outboard end or the middle and the end of the boom are also supported from the pinnacle by mechanical links 25 when the boom is lowered to level and the wire rope boom hoist reeving 23 is slack. The wire rope hoist reeving which raises the boom takes the load off the links which collapse when the cantilevered boom is rotated to its stowed position about its hinge point 27 at its inboard end proximate the superstructure.
While, in most typical dockside applications, the gantry of a cargo container handling crane is a horizontally slidable or a raisable cantilever boom, some gantries are single beam while most others are dual girder beam. The present invention can be utilized on any of these basic types of gantry crane designs. All of these cranes are similar to the '981 gantry type crane in that they employ a movable cargo container lift trolley 29 mounted on rails on the crane gantry sections 11 & 17, usually with a suspended operator's cab 31. The trolleys shuttle along rails usually mounted on top of, inside of, or below the crane gantry. The trolley suspends a cargo container lifting spreader 33 below the gantry. In the case of the dual girder beam gantry, the load is suspended through the center of the gantry between the gantry side girders which extend for the length of the gantry. For a single beam gantry, the trolley is suspended on rails usually mounted below the beam. The cargo container lifting spreaders are releasably suspended from the trolley, which carries the wire rope suspension sheaves for the fleet-through wire rope load hoist reeving, by means of a detachable headblock 35. Different length spreaders can be secured to the headblock to accommodate correspondingly different size containers.
The headblock 35 and spreader 33 can be raised or lowered from the crane gantry 11, 17 by the operator in the cab 31 to engage cargo containers which are located on the dock or shipboard. The spreader permits the containers to be lifted by the trolley 29 for transport along the gantry between the pickup and deposition areas 19 in a cargo container transport ship, or under the crane, or under its backreach. The trolley is reciprocated along the gantry by a continuous wire rope drive system, and the headblock is raised and lowered by a load hoisting wire rope system, both which are usually driven by wire rope drums located in a machinery house 37.
However, there are several types of wire rope reeving and trolley drives utilized in the prior art relating to effecting cargo container transfer. These include the trolley rope drives and load hoist wire ropes. The latter of these two systems primarily benefits from the implementation of the present invention, but the trolley drive ropes can also. These wire rope systems are each disclosed in the accompanying prior art drawings which illustrate typical apparatus for both the wire rope reeving for a rope drive trolley for a shoreside cargo container handling crane and a wire rope load hoisting system driven from a remote location on a crane. There is a problem with these large cranes which relates to wire rope sag and, in particular, with respect to sag in the load hoist wire rope system. When the hoist trolley traverses to the maximum outreach position, the unsupported rope span between the main hoist rope sheave on the trolley, and the hoist rope support sheave at the opposite end of the gantry, reaches a maximum. Under this condition, the hoist ropes will have a maximum sag because of the unsupported dead weight of the wire ropes. This catenary effect will become excessive when there is no load under the lifting spreader. The container load generates a downforce in the wire rope system that provides a tension force in the horizontal ropes that restrains rope sag. For cranes with higher rated lifting capacities, the main wire rope diameters are larger to handle the increased loads. Consequently, the main hoist ropes are heavier and the suspended ropes have greater sag.
The most unfavorable condition for rope sag is when the main trolley is positioned at the furthest outreach position, and when the main hoist drum has payed out the most rope in order to lower the spreader to engage a container in the hold of a ship. When the spreader is landed on the container, the main hoist ropes have the greatest slack because there is no load on the rope to maintain the tension required to minimize rope sag. The sag under these conditions can be as much as 30 feet. When the operator commences to lift an engaged container, the force created by the lifting load will suddenly take up the slack ropes generating a “rope whipping effect.” This causes the ropes to bounce and to slap on the adjacent structure of the crane frame, which in turn causes structural damage as well as premature fatigue failure of the wire ropes. Sometimes the ropes will actually engage and detach a berthed ship structural element. The damaged structure can fall onto the top of the ship deck to cause further property damage and possibly personal injury or death to workers or crew. The bouncing rope also generates nuisance noise and an unsafe operating condition and can injure personnel if they happen to be near the bouncing ropes. Conversely, the same condition occurs in reverse: when a load is released under the predescribed most unfavorable condition, the same whipping effect results from the release of tension. The maximum inboard backreach retracted position of the trolley also causes an unfavorable rope sag condition and can create a whipping effect.
For those cranes built before 1985, the catenary effect on the wire rope was not severe enough to raise the operator's concern. However, as the container ships have been getting larger in size, the cranes have correspondingly become larger with boom outreaches extending further. As a result, the rail gauge for the crane dockside tracks have expanded from 50 feet to 100 feet to provide better crane operational stability against the possibility of the crane tipping over during load lifting. The unsupported wire rope span is therefore longer than prior art cranes, and this means that the main hoist ropes unsupported span becomes much more than the older cranes. Consequently, the crane lifting capacities are becoming higher requiring the use of still heavier main hoist wire ropes. This compounds the problem and creates still greater rope sag. As a result, the rope sag catenary effect has now become excessive and has created an identified safety problem.
Reference is made to FIG. 2 for an illustration of a first type of basic wire rope reeving support system utilized to alleviate the rope sag problem. It employs a pair of catenary rope support trolleys 39, 41 on the gantry 17 which are disposed on opposite sides of the main hoist trolley 29 to support the wire ropes. In this typical type of crane, the previously described two independent rope systems can be utilized: a trolley drive system and the load hoist system. Only the latter or load hoist system is shown in FIG. 2 of the drawings for clarity because some cranes do not utilize a wire rope drive system for the main trolley drive as will be explained.
Reference is made to FIG. 3 which shows the typical reeving for a main trolley traversing drive system for gantry cranes which has been omitted from FIG. 2. In the normal configuration of wire rope reeving for the drive system, a pair of continuous traversing or wire drive ropes 43 are secured to opposite ends of the cargo transport trolley 29 and are driven by one or a pair of trolley drive drums 45. The term “continuous” generally means the wire rope is a continuous loop. Portions of the rope are either towing or slack depending on the direction of movement of the trolley, and the rope is always active and continuously in motion when the trolley moves.
For the “rope trolley” type of crane of FIG. 3, the drive drums 45 for the two pairs of main trolley drive ropes 43 are usually located somewhere mid-span on the gantry 17 in a machinery house 37 (FIG. 1). The pairs of drive ropes are oppositely wound and extend from the drums to reversing sheaves 47 disposed at opposite ends of the gantry through hydraulic rope tensioners 49. The pairs of ropes reverse direction in the reversing sheaves and extend to opposite ends of the cargo container transport trolley 29 which is movably located anywhere along the gantry. Operation of the drive drums moves the trolley in one direction along the gantry while reverse rotation of the drive drums reverses the tension and slack forces in the drive ropes and the movement of the trolley.
Reference is made again to FIG. 2. In addition to the trolley drive ropes (of FIG. 3) in a “rope trolley” cargo container handling crane, a separate system of load hoist or lift ropes 51 for the lifting spreader 33 are integrated into the wire rope reeving system. They are very similar in orientation, operation, and location to the trolley drive ropes in the sense that they are also driven from a remote location by drive drums 53 located in a machinery house and run through reversing sheaves 47 at one end of the crane gantry 17. They differ, however, in that the two pairs of hoist ropes are not secured to the main trolley 29 but are reeved through fleet-through hoist sheaves 55 mounted thereon whereby they travel downward from the hoist sheaves to the headblock 35, around suspension sheaves on the headblock, back up to the trolley, around fleet through additional hoist sheaves on the trolley, and outboard therefrom to the end of the gantry where they are dead-ended 57 at the opposite end of the gantry from the reversing sheaves 47. The ropes may be multiply-reeved between the headblock and the trolley sheaves to obtain a greater mechanical advantage. The hoist ropes operate independent of the trolley drive ropes and can be static or moving as the trolley moves along the gantry depending on whether the lifting spreader headblock for the containers is being lifted or lowered concurrently while the trolley moves.
A second type of wire rope reeving for a crane can be called a “machine trolley” container crane. The hoisting machinery and the trolley traversing machinery are both mounted on the trolley. The wire ropes from the drums of the hoist machinery mounted on the trolley go down to reversing sheaves on the lifting spreader headblock and then go back up to the trolley and are dead-ended to it. The trolley traversing machinery drives the trolley wheels to move the trolley along the rails on the girder or boom of the gantry crane.
A third type of wire rope reeving can be called a “semi-rope trolley” container crane. It is a combination of the first two types. The load hoist machinery is located in the machinery house on the gantry and the wire ropes are reeved the same as for the “rope trolley” crane of FIG. 2. However, the gantry traversing machinery for the trolley is mounted thereon the same as the “machine trolley” type container crane described above.
The latter two types of prior art cranes have the following disadvantages. In both cases, the trolley traversing machinery is mounted on the trolley, and in the second type the hoisting machinery as well. The trolley becomes extremely heavy and the crane gantry girder structure required to support the trolley must necessarily be made stronger and thereby heavier. In addition, as the trolleys are driven by the wheels interconnected to the trolley traversing machinery, the wheels sometimes slip in foul conditions such as the beginning of rainfall or when the rails have early morning frost.
For the “rope trolley” type of crane, the trolley carries only fleet through sheaves and it does not have either hoisting machinery or trolley traversing drive machinery mounted on it. Therefore, the rope trolley structure is the lightest possible weight in comparison, and the trolley supporting crane structure can be built correspondingly of minimum weight. Because the rope trolley is towed by the drive ropes, there is no wheel slip. However, as the long length of the wire ropes for the hoist machinery and the trolley traversing machinery are reeved from the machinery house to both of the girder ends and to the trolley, the wire ropes experience considerable sag and wear and incur higher maintenance costs.
In order to mitigate the rope sag problem, various solutions have been utilized. Reference is again made to FIG. 2 wherein a first solution has been shown employing a pair of catenary rope support trolleys. A waterside catenary trolley 41 is installed between the main trolley 29 and the boom tip equalizer platform. A landside catenary trolley 39 is also installed between the main trolley and the trolley girder end tie on the opposite side of the main trolley from the waterside catenary trolley. As the rope trolley is moved by the towing ropes to the waterside greatest outreach position, the landside catenary trolley is pulled by the main trolley and moves to the mid span distance between the trolley girder end tie and the main trolley frame. By doing this, the landside catenary trolley provides a support for the main hoist wire ropes and the trolley towing ropes which decreases the rope sag in both to 25 percent of the original sag. As the main trolley moves back to the furthest landside backreach position, the waterside catenary trolley is pulled by the main trolley and travels to the mid span distance between the boom tip equalizer platform and the main trolley to provide the rope support for the waterside trolley drive and hoist ropes as did the landside catenary trolley. The catenary trolleys are actuated by an unpowered continuous wire rope system engaged with the main trolley. As the main trolley moves, the catenary trolleys move in unison. A rope tensioning system is also provided to eliminate rope slack and to help keep rope tension in the catenary rope reeving system.
There are several disadvantages to the catenary trolley rope support system:
1. The added catenary trolleys (at least two) add substantial expense to the construction of the crane not only for their cost but for the increased size of the gantry girders required to support the added weight. The main trolley drive system must tow the catenary trolleys during all traversing motion. This increases the power requirements of the main trolley drive system and decreases the efficiency of the crane.
2. The waterside catenary trolley is positioned on the gantry between the main trolley and the boom tip equalizer sheaves. This means that increased cost for extra boom length (between 5 to 7 feet) is required to permit insertion of the waterside catenary trolley. Because the boom of the crane must be raised to the stowed position when the crane is not in operation, the boom hoist mechanism is required to lift up the extra boom length weight plus the additional weight of the waterside catenary trolley. As a result, the size of the boom hoist mechanism required for the boom lifting system must also be increased. These additional increased costs include larger electrical motors, larger gear reduction units, and all the necessary couplings and associated equipment.
A landside catenary trolley is placed between the main trolley and the girder end sheaves. This also means that extra inboard end girder and rail length (between 8 to 10 feet) is required to contain the landside trolley. This extension will also add weight as well as substantial cost to the crane for the additional trolley and gantry length and strength.
3. A catenary trolley rope support system requires the installation of additional pairs of towing ropes, the catenary trolley sheaves and clamps on the main trolley, and a hydraulic tensioning system. Because it is a hydraulic system, it is not environmentally friendly due to the possible leakage of oil to the ground and to the water. This adds to the service and maintenance requirements for those items. All of the ropes require frequent lubrication. To service the towing ropes and sheaves, several maintenance access platforms must be installed. The two catenary trolleys also require access platforms to perform the maintenance such as to change bearings, axles, and wheels.
4. The waterside catenary trolley is necessarily located between the boom hinge point and the boom tip equalizer platform. When the main trolley is at the parking position somewhere intermediate the gantry between the boom hinge point and the rear girder tie, the waterside catenary trolley is located on the boom somewhere mid-span from the boom hinge point to the boom tip equalizer platform. When the boom is raised to the stowed position, the waterside catenary trolley is lifted up with the boom and hung in the air supported by the catenary tow ropes. This adds a safety concern about should the ropes fail. Rope failure will permit the catenary trolley to drop to the ground or on top of the ship deck to cause severe property damage and possible personal injury. No safety locks or stops can arrest three tons of descending trolley weight which can exceed 100 mph impact speed.
5. In some cases, crane operators request the capability for the main trolley to traverse between the legs of the crane while the boom is raised to the stowed position. This complicates the operation of the waterside catenary trolley since it must be powered to move up and down along the trolley rails with the boom projecting upward at an 84 degree angle. This increases the power requirements as well as the safety concerns for this system.
6. The total manufacturing and maintenance costs for the catenary trolley rope support systems, including the required extra boom and girder lengths, two catenary trolleys, sheaves, wheels, axles, reeving of the towing ropes, hydraulic cylinders, the rope tensioning system, and higher boom lifting horsepower required to lift the heavier boom with a catenary trolley, is very high.
Reference is made to FIG. 4 which shows another type of rope support system which utilizes multiple fixed position rope support rollers 59 mounted on the gantry girders. This system requires installing multiple reversing sheaves 61 on the main trolley frame 29 and requires employing several reverse rope bends in a short distance on the main hoist ropes which shortens the hoist rope life significantly. This rope reeving arrangement could reduce the main hoist rope fatigue life to 50 percent or less than the original life without the rope support system. The rope fatigue life is determined by how many wire strands are allowed to break before mandatory rope replacement for operational safety concerns. This is costly due to the operation losses and maintenance costs. As a result, this system has not proved practical in the container crane industry.
The present invention provides an improvement in wire rope support systems for a crane's wire rope reeving which reduces the effects of the disadvantages in the prior types of similar crane wire rope support systems.